1. Field of the Invention
The present invention relates to a pivot assembly bearing and a hard disk drive device.
2. Description of the Related Art
A hard disk drive device is one of storage devices for computers. For example, in the hard disk drive device, a swing arm is supported by a pivot assembly bearing in a swingable manner. The pivot assembly bearing is configured such that a pair of rolling bearings is arranged between a shaft and a sleeve surrounding the shaft, and is fixed to a base plate with a screw.
In recent years, as an amount of recording data increases and a data reading/writing speed increases, it becomes increasingly important to maintain cleanliness inside the hard disk drive device. Examples of foreign matters generated in the hard disk drive device include particles due to a lubricant such as grease used for the rolling bearing of the pivot assembly bearing. The particles are minute amount of particles of oil in the lubricant discharged to the outside when a rolling element of the rolling bearing is rotated to stir the lubricant enclosed in the rolling bearing. When the particles float, the particles adhere to components of the hard disk drive device and exert an adverse effect on the hard disk drive device. To reduce the particles to be discharged, various pivot assembly bearings have been developed.
As such a pivot assembly bearing, for example, Japanese Laid-open Patent Publication No. 2013-48005 discloses a pivot assembly bearing (a pivot bearing unit for a hard disk actuator) having a shield cap with a stepped shape, the shield cap being arranged to face an outer ring of the rolling bearing constituting the pivot assembly bearing in an axial direction, in order to narrow a gap between the shield cap and the outer ring of the rolling bearing for reducing the amount of discharged particles.
Japanese Laid-open Patent Publication No. 1-277375 (the invention of a magnetic disc device) discloses a bearing structure for preventing diffusion of contaminants by providing a magnetic fluid seal containing a plurality of bearings between a shaft and an arm holder in a magnetic disc device including the arm holder rotatably held by the shaft via the bearings.
However, in the pivot assembly bearing disclosed in Japanese Laid-open Patent Publication No. 2013-48005, there is a large gap between the shield cap and a shielding member of the rolling bearing, so that a flow of air entering or exiting through the gap is generated when a strong air flow is caused inside the hard disk drive device due to rotation of the magnetic disc or a swing movement of the swing arm. In this case, the air flowed out from the inside of the pivot assembly bearing passes through a portion of the rolling bearing in which the lubricant is enclosed. Due to this, the lubricant in the rolling bearing may be discharged as particles along with the air that is flowed out. Thus, in terms of reducing the discharged particles, further improvement is required.
In the bearing structure disclosed in Japanese Laid-open Patent Publication No. 1-277375, an internal pressure is increased when the air inside the pivot assembly bearing is expanded due to heat caused by the operation of a motor or heat caused when the swing arm repeatedly swings for a long time, and a magnetic fluid of the magnetic fluid seal may be scattered.